sip (session initiation protocol) - sip messages

SIPSIP(Session Initiation Protocol)(Session Initiation Protocol)- SIP Messages- SIP Messages

ContentsContents A Simple SIP Example SIP Message

- Request Message RFC2543 (INVITE, REGISTER, BYE, ACK, CANCEL,OPTION)

INTERNET-DRAFTS (INFO, PRACK)

- Response Message

A Simple SIP Example(1)A Simple SIP Example(1)Marconi

INVITE

180 Ringing

200 OK

ACK

Media Session

BYE

200 OK

Tesla

A Simple SIP Example(2)A Simple SIP Example(2)

Via: SIP/2.0/UDP lab.high-voltage.org:5060To: G. Marconi <sip:Marconi@radio.org>From: Nikola Tesla <sip:n.tesla@high-voltage.org>Call-ID: 123456789@lab.high-voltage.orgCSeq: 1 INVITESubject: About That Power Outage…Contact: sip:n.tesla@high-voltage.orgContent-type: application/sdpContent-Length: 158

Via: SIP/2.0/UDP lab.high-voltage.org:5060To: G. Marconi <sip:Marconi@radio.org>From: Nikola Tesla <sip:n.tesla@high-voltage.org>Call-ID: 123456789@lab.high-voltage.orgCSeq: 1 INVITESubject: About That Power Outage…Contact: sip:n.tesla@high-voltage.orgContent-type: application/sdpContent-Length: 158

INVITE sip:marconi@radio.org SIP/2.0INVITE sip:marconi@radio.org SIP/2.0

v=0o=Tesla 2890844526 2890844526 IN IP4 lab.high-voltage.orgs=Phone Callc=IN IP4 100.101.102.103t=0 0m=audio 49170 RTP/AVP 0a=rtpmap:0 PCMU/8000

v=0o=Tesla 2890844526 2890844526 IN IP4 lab.high-voltage.orgs=Phone Callc=IN IP4 100.101.102.103t=0 0m=audio 49170 RTP/AVP 0a=rtpmap:0 PCMU/8000

Start line

Message Header

Message Body

CRLF

minimum requiredheader set

A Simple SIP Example(3)A Simple SIP Example(3)SIP/2.0 180 RingingSIP/2.0 180 Ringing

Via: SIP/2.0/UDP lab.high-voltage.org:5060To: G. Marconi <sip:Marconi@radio.org>From: Nikola Tesla <sip:n.tesla@high-voltage.org>Call-ID: 123456789@lab.high-voltage.orgCSeq: 1 INVITEContent-Length: 0

Via: SIP/2.0/UDP lab.high-voltage.org:5060To: G. Marconi <sip:Marconi@radio.org>From: Nikola Tesla <sip:n.tesla@high-voltage.org>Call-ID: 123456789@lab.high-voltage.orgCSeq: 1 INVITEContent-Length: 0

- Copying many of the Headers from the INVITE message,

including the Via, To, From, Call-ID, and CSeq

- To and From headers are not reversed(To and From headers

are Defined to indicate the direction of the request)

A Simple SIP Example(4)A Simple SIP Example(4)

..Contact: sip:marconi@radio.orgContent-type: application/sdpContent-Length: 155

..Contact: sip:marconi@radio.orgContent-type: application/sdpContent-Length: 155

SIP/2.0 200 OKSIP/2.0 200 OK

v=0o=heisenberg 2890844526 2890844526 IN IP4 200.201.202.203s=Phone Callc=IN IP4 200.201.202.203t=0 0m=audio 49172 RTP/AVP 0a=rtpmap:0 PCMU/8000

v=0o=heisenberg 2890844526 2890844526 IN IP4 200.201.202.203s=Phone Callc=IN IP4 200.201.202.203t=0 0m=audio 49172 RTP/AVP 0a=rtpmap:0 PCMU/8000

UAS Media Capability

- When the called party decides to accept the call, a 200 OK response is sent

A Simple SIP Example(5)A Simple SIP Example(5)

ACK sip:marconi@radio.org SIP/2.0ACK sip:marconi@radio.org SIP/2.0

Via: SIP/2.0/UDP lab.high-voltage.org:5060To: G. Marconi <sip:marconi@radio.org>From: Nikola Tesla <sip:n.tesla@high-voltage.org>Call-ID: 123456789@lab.high-voltage.orgCSeq: 1 ACKContent-Length: 0

Via: SIP/2.0/UDP lab.high-voltage.org:5060To: G. Marconi <sip:marconi@radio.org>From: Nikola Tesla <sip:n.tesla@high-voltage.org>Call-ID: 123456789@lab.high-voltage.orgCSeq: 1 ACKContent-Length: 0

- ACK Method means that UAC can support the media session proposed by UAS- At this point , the media session begins using the media information carried in the SIP messages.- In TCP , connection is safely closed after sending ACK Method

A Simple SIP Example(6)A Simple SIP Example(6)BYE sip:n.tesla@high-voltage.org SIP/2.0BYE sip:n.tesla@high-voltage.org SIP/2.0

Via: SIP/2.0/UDP tower.radio.org:5060To: Nikola Tesla <sip:n.tesla@high-voltage.org>

From: Marconi <sip:marconi@radio.org>Call-ID: 123456789@lab.high-voltage.orgCSeq: 1 BYEContent-Length: 0

Via: SIP/2.0/UDP tower.radio.org:5060To: Nikola Tesla <sip:n.tesla@high-voltage.org>

From: Marconi <sip:marconi@radio.org>Call-ID: 123456789@lab.high-voltage.orgCSeq: 1 BYEContent-Length: 0

SIP/2.0 200 OKSIP/2.0 200 OK

.. ..

.. ..

- SIP-enabled device must contain both SIP server and SIP client software

- To and From headers are reversed but Tesla is able to identify the call leg and tear down the correct media session

SIP MessagesSIP Messages Method(RFC2543)

- INVITE, REGISTER, BYE, ACK, CANCEL, OPTIONS

Internet-Drafts Method - INFO, PRACK

Response Messages

INVITE methodINVITE method Establish media sessions between user agents It usually has a message body containing the media info

rmation- If it dose not have, the ACK contains the media information

re-INVITE- An INVITE sent for an existing call leg references the same Call-ID as the original INVITE- Changing the session characteristics.- CSeq is incremented

Request-URI is able to contain a phone number ex) INVITE <sip:411@salzburg.aut>;user=phone SIP/2.0

REGISTER methodREGISTER method

The REGISTER method is used by a user agent to notify a SIP network of its current IP address and the URLs for which it would like to receive calls

Request-URI contains only the domain of the registrar Server with no user portion Example(Contact, Expires header & expires parameter)

REGISTER sip:registrar.munich.de SIP/2.0..Contact: sip:werner.heisenberg@munich.de

200 OK

Contact: *Expires: 0

Contact: sip:galvani@bologna.edu.it;expires=30

Contact: sip:galvani@bologa.edu.it;Expires: 30

BYE methodBYE method It is used to terminate an established media session A BYE is send only by user agents participating in the sess

ion, never by proxies or other third parties A BYE can be sent by either the caller or the called party i

n a session. BYE always increments the CSeq

ACK methodACK method The ACK method is used to acknowledge final responses t

o INVITE requests ACK is never incremented for an ACK - A UAS can match the CSeq number of the ACK with the n

umber of the corresponding INVITE An ACK may contain an message body, but can not be use

d to modify a media description

CANCEL method(1)CANCEL method(1) The CANCEL method is used to terminate pending

searches or call attempts A forking proxy can use the CANCEL method.

Calling user agent

Forking proxy server

The CANCEL method dose not increment the CSeq

- UA can match the CSeq of the CANCEL with the CSeq of the pending INVITE

CANCEL method(2)CANCEL method(2) CANCEL method is a hop-by-hop request If a final response has already been received, a user agent should not

generate a CANCEL

INVITECSeq: 1 INVITE INVITE

CSeq: 1 INVITE 100 TryingCSeq: 1 INVITE

100 TryingCSeq: 1 INVITE

CANCELCSeq: 1 CANCEL

200 OKCSeq: 1 INVITE

200 OKCSeq: 1 CANCEL

CANCELCSeq: 1 CANCEL

200 OKCSeq: 1 INVITE

200 OKCSeq: 1 CANCEL

ACKCSeq: 1 ACK

BYECSeq: 2 BYE

200 OKCSeq: 2BYE

UAC Stateful Proxy UAS

OPTIONS methodOPTIONS method The OPTION method is used to query a user agent or

server about its capabilities and discover its current availability

OPTIONS sip:proxy.carrier.com SIP/2.0Via: SIP/2.0/UDP cavendish.kings.cambridge.edu.ukTo: sip:proxy.carrier.comFrom: J.C. Maxwell <sip:james.maxwell@kings.cambridge.edu.uk>CSeq: 1 OPTIONSContent-Length: 0

SIP/2.0 200 OKVia: SIP/2.0/UDP cavendish.kings.cambridge.edu.uk;tag=512A6To: sip:proxy.carrier.comFrom: J.C. Maxwell <sip:james.maxwell@kings.cambridge.edu.uk>Call-ID: 9352812@cavendish.kings.cambridge.edu.ukCseq: 1 OPTIONSAllow: INVITE, OPTION, ACK, BYE, CANCEL, REGISTERAccept-Language: en, de, frContent-Length: 0

INFO & PRACK method(1)INFO & PRACK method(1) INFO method

- It is used by UA to send call signaling information to another user agent with which it has an established media session.

PRACK

- It is used to acknowlegde receipt of reliably transported provisional responses(1XX)

INFO & PRACK method(2)INFO & PRACK method(2)

UAC UASINVITESupported:100relCSeq: 1 INVITE

100 TryingCSeq: 1 INVITE

180 RingingCSeq: 1 INVITERSeq: 314 T1

180 RingingCSeq: 1 INVITERSeq: 314 PRACK

CSeq: 2 PRACKRAck: 314 1 INVITE

200 OKCSeq: 2 PRACK 200 OK

CSeq: 1 INVITEACKCSeq: 1 ACK

Media Session

Response Messages(1)Response Messages(1) A SIP response is a message generated by a UAS or a SIP

server to reply to a request generated by a UAC The reason phrase is for human consumption only - 200 Call Failed = 200 OK

Informational class response(1XX)

- It is used to indicate call progress - The first informational response received by the UAC confirms receipt

of the INVITE, and stops retransmission of the INVITE ( ex)180 Ringing)

Response Messages(2)Response Messages(2) Success 200 OK

- When used to accept a session invitation( ex) INVITE )- Successful completion of the request( ex) PRACK )

Redirection class response(3XX) - It is generally sent by a SIP server acting as a redirect server in response to an INVITE - There is no requirement that a UAC receiving a

redirection response must retry the request to the specified address. - UAC could be configured to automatically generate a new INVITE upon receipt of a redirection class response without requiring user intervention

Response Messages(3)Response Messages(3) Client Error(4XX) - It is used by a server or UAS to indicate that the request cannot be

fulfilled as it was submitted

- 400 Bad Request , 401 Unauthorized, 404 Not Found ..

Server Error(5XX) - The request cannot be processed because of an error with the server

- The response may contain a Retry-After header if the server anticipates

being available within a specific time period

- 501 Not Implemented, 505 Version Not Supported

Response Messages(4)Response Messages(4) Global Error(6XX) - The Server knows that the request will fail wherever it is tried. As a

result the request should not be sent to other locations

- 604 Dose Not Exist Anywhere

It is similar to the 404 Not found but indicates that the user in the Request-URI cannot be found anywhere.